1. Field of the Art
The present invention relates in general to a solid memory medium, and more particularly to such a memory medium which comprises a solid storage portion formed of a pyroelectric and electro-optic material and an apparatus for reading information from the memory medium.
2. Related Art Statement
There are known a magnetic and a magneto-optical memory medium both of which are preferably used for writing thereon and reading therefrom a comparatively large amount of information. As to the magnetic memory medium, which is usually used in the form of a floppy disk or hard disk, information is written through magnetization of the magnetic layer, and the information stored is read out by a magnetic head. As to the magneto-optical memory medium or a magneto-optical disk, information is magnetically recorded on the disk, and the information recorded is optically retrieved.
3. Problems Solved by the Invention
However, all of the conventional memory media including the magnetic and magneto-optical memory media, have a problem of an insufficient density of information, that is, a comparatively small number of data bits per unit area of a memory medium. Those memory media provide another problem in that an apparatus needed for reading information from such a memory medium requires a large number of parts or elements.
In the above-indicated situation, the inventors have conducted various studies and investigations, and revealed that a pyroelectric and electro-optic material can be used as a memory medium. More specifically described, information is written on such a material through local residual polarization thereof owing to the pyroelectrical property of the material. The local residual polarization is caused by positive and negative electric charges which are locally generated by local heating of the material. The thus-stored information is retrieved by means of taking advantage of variation in refractive index of the material due to the local residual polarization. The variation in the refractive index is based on the electro-optical property of the material.